Israel’s Supreme Court heard the first challenge Tuesday to Prime Minister Benjamin Netanyahu’s contentious judicial overhaul, deepening a showdown with the far-right government that has bitterly divided the nation and put it on the brink of a constitutional crisis.

Netanyahu’s coalition, a collection of ultranationalist and ultrareligious lawmakers, unveiled the overhaul earlier this year, saying it was necessary to rein in an unelected judiciary they believe wields too much power.

Critics say the plan — which would weaken the Supreme Court — is a profound threat to Israeli democracy and that it would concentrate power in the hands of Netanyahu and his allies.

They say the court is a key counterweight on majority rule in a country with an otherwise weak system of checks and balances — with just one house of parliament where the governing coalition is headed by the prime minister. The country’s president has largely ceremonial powers, and there is no firm, written constitution.